Substrate for flexible display and method of manufacturing the substrate

ABSTRACT

A substrate for a flexible display is disclosed. The substrate has a film stress range that does not affect an electronic device such as a thin film transistor, and includes a barrier layer having excellent oxygen and moisture blocking characteristics, and a method of manufacturing the substrate. The substrate includes: a plastic substrate having a glass transition temperature from about 350° C. to about 500° C.; and a barrier layer disposed on the plastic substrate, having a multi-layer structure, wherein at least one silicon oxide layer and at least one silicon nitride layer are alternately stacked on each other, and having a film stress from about −200 MPa to about 200 MPa due to the at least one silicon oxide layer and the at least one silicon nitride layer.

CROSS-REFERENCE TO RELATED PATENT APPLICATION

This application claims the benefit of Korean Patent Application No. 10-2010-0074979, filed on Aug. 3, 2010, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present disclosure relates to a substrate for a flexible display, and a method of manufacturing the substrate.

2. Description of the Related Art

Markets of liquid crystal display devices and organic light emitting display devices are currently expanding to displays of digital cameras, video cameras, and mobile devices, such as personal digital assistants (PDAs) and mobile phones. The displays of mobile devices need to be thin, light, and moreover, unbreakable. In order to form a thin and light display, a method of preparing a display by using a conventional glass substrate, and then thinning the glass substrate mechanically or chemically has been introduced, besides a method of preparing a display by using a thin glass substrate. However such methods are complicated and the glass substrate may easily break, and thus the methods are difficult to be actually used. Also, for the mobile devices to be easily carried and to be applied to display devices of various shapes, the displays may be flexible to realize a curved surface. However, it is difficult for the conventional glass substrate to have flexibility.

Accordingly, there have been attempts to manufacture a display device by using a plastic substrate, but the plastic substrate has high level of moisture and oxygen penetration and is not suitable for a high temperature process.

SUMMARY OF THE INVENTION

One aspect of the present invention provides a substrate for a thin, flexible display, which has film stress range that does not affect an electronic device, such as a thin film transistor, and includes a barrier layer having excellent oxygen and moisture blocking characteristics, and a method of manufacturing the substrate.

According to the aspect of the present invention, the substrate including: a plastic substrate having a glass transition temperature from about 350° C. to about 500° C.; and a barrier layer disposed on the plastic substrate, having a multi-layer structure, wherein at least one silicon oxide layer and at least one silicon nitride layer are alternately stacked on each other, and having a film stress from about −200 MPa to about 200 MPa due to the at least one silicon oxide layer and the at least one silicon nitride layer.

The barrier layer may include: a first silicon oxide layer; a silicon nitride layer stacked on the first silicon oxide layer; and a second silicon oxide layer stacked on the silicon nitride layer.

The barrier layer may include: a first silicon oxide layer; a first silicon nitride layer stacked on the first silicon oxide layer; a second silicon oxide layer stacked on the first silicon nitride layer; a second silicon nitride layer stacked on the second silicon oxide layer; and a third silicon oxide layer stacked on the second silicon nitride layer.

The barrier layer may include: a first silicon oxide layer; a first silicon nitride layer stacked on the first silicon oxide layer; a second silicon oxide layer stacked on the first silicon nitride layer; a second silicon nitride layer stacked on the second silicon oxide layer; a third silicon oxide layer stacked on the second silicon nitride layer; a third silicon nitride layer stacked on the third silicon oxide layer; and a fourth silicon oxide layer stacked on the third silicon nitride layer.

The at least one silicon oxide layer included in the barrier layer may have compressive film stress. The at least one silicon nitride layer included in the barrier layer may have tensile film stress.

The at least one silicon nitride layer may have a film density from about 2.5 g/cm³ to about 2.7 g/cm³.

The at least one silicon nitride layer may have a hydrogen atom content from about 13% to about 17%.

Each of the at least one silicon nitride layer may have a thickness from about 200 Å to about 1000 Å.

Each of the at least one silicon oxide layer may have a thickness from about 1000 Å to about 3000 Å.

The plastic substrate may include at least one of polyimide, polycarbonate, polyphenylene sulfide, and poly(arylen ether sulfone.

According to another aspect of the present invention, there is provided a method of manufacturing a substrate for a flexible substrate, the method including: providing a plastic substrate having a glass transition temperature from about 350° C. to about 500° C.; and forming a barrier layer having a film stress from about −200 MPa to about 200 MPa by alternately stacking at least one silicon oxide layer and at least one silicon nitride layer on the plastic substrate.

The forming of the barrier layer may include high temperature deposition at a temperature from about 350° C. to about 400° C.

The barrier layer may include: a first silicon oxide layer; a silicon nitride layer stacked on the first silicon oxide layer; and a second silicon oxide layer stacked on the silicon nitride layer.

The barrier layer may include: a first silicon oxide layer; a first silicon nitride layer stacked on the first silicon oxide layer; a second silicon oxide layer stacked on the first silicon nitride layer; a second silicon nitride layer stacked on the second silicon oxide layer; and a third silicon oxide layer stacked on the second silicon nitride layer.

The barrier layer may include: a first silicon oxide layer; a first silicon nitride layer stacked on the first silicon oxide layer; a second silicon oxide layer stacked on the first silicon nitride layer; a second silicon nitride layer stacked on the second silicon oxide layer; a third silicon oxide layer stacked on the second silicon nitride layer; a third silicon nitride layer stacked on the third silicon oxide layer; and a fourth silicon oxide layer stacked on the third silicon nitride layer.

The at least one silicon oxide layer included in the barrier layer may have compressive film stress. The at least one silicon nitride layer included in the barrier layer may have tensile film stress.

The at least one silicon nitride layer may have a film density from about 2.5 g/cm³ to about 2.7 g/cm³.

The at least one silicon nitride layer may have a hydrogen atom content from about 13% to about 17%.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which:

FIG. 1 is a cross-sectional view of a substrate for a flexible display, according to an embodiment of the present invention;

FIG. 2 is a cross-sectional view of a substrate for a flexible display, according to another embodiment of the present invention;

FIG. 3 is a cross-sectional view of a substrate for a flexible display, according to another embodiment of the present invention;

FIGS. 4 through 6 are diagrams for describing a method of manufacturing a display device by using the substrate of FIG. 1, according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

While the invention have numerous embodiments, only some of such embodiments will be illustrated in the drawings and described in detail in the written description. The present invention is not limited to the particular embodiments, and there are changes, modifications and substitutes that do not depart from the spirit and technical scope of the present invention.

While terms of “first,” “second,” “third,” etc., are used to describe various components, such terms do not carry the meaning of order. These terms are used only to distinguish one component from another. Also, in the present specification, the terms of “including” and “having,” are intended to mean “comprising” so as to indicate the possibility of existence of any additional features, numbers, steps, actions, components, parts, or combinations.

Now, various features of the present invention will be described more fully with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown.

FIG. 1 is a cross-sectional view of a substrate 1000 for a flexible display, according to an embodiment of the present invention.

The substrate 1000 according to the current embodiment of the present invention includes a plastic substrate 50, and a barrier layer 100 disposed on the plastic substrate 50.

The plastic substrate 50 has flexibility enough to realize a flexible display. Also, the plastic substrate 50 may have a thin film structure for the flexibility.

The plastic substrate 50 may have a glass transition temperature (Tg) from about 350° C. to about 500° C. With this feature, the plastic substrate 50 can stably perform functions of a substrate without being deformed even when the barrier layer 100, a thin film transistor, and an electronic device are formed on the plastic substrate 50 at high temperature. In detail, the barrier layer 100 is formed at a temperature from about 350° C. to about 400° C. Accordingly, if the Tg of the plastic substrate 50 is less than about 350° C., the plastic substrate 50 may change to a rubber having elasticity at about 350° C. and thus may be unable to perform the functions of substrate. On the other hand, the plastic substrate 50 having the Tg exceeding about 500° C. has bad processability.

The plastic substrate 50 may be formed of a polymer having high thermal resistance. For example, the plastic substrate 50 may include at least one material selected from the group consisting of polyethersulfone (PES), polyacrylate (PAR), polyetherimide (PEI), polyethylene naphthalate (PEN), polyethylene terephthalate (PET), polyphenylene sulfide (PPS), polyarylate, polyimide (PI), polycarbonate (PC), cellulose triacetate (TAC), cellulose acetate propionate (CAP), and poly(arylen ether sulfone) as a type of engineering plastic. Specifically, PI has excellent mechanical strength and has better thermal resistance than other polymers as the Tg of PI is about 450° C. Accordingly, even when the barrier layer 100 is disposed on the plastic substrate 50 including PI at high temperature, the plastic substrate 50 may stably perform the functions of a substrate without drooping due to a weight of the barrier layer 100. Also, the plastic substrate 50 including at least one of the above polymers has high level of oxygen and moisture penetration. Accordingly, when a thin film transistor and an electronic device are directly formed on the plastic substrate 50, the thin film transistor and the electronic device may be exposed to oxygen and moisture penetrating through the plastic substrate 50, and thus lifetime of a display may be remarkably reduced. The barrier layer 100 is provided for blocking the moisture and oxygen formed on the plastic substrate 50.

In embodiments, the barrier layer 100 is formed on the plastic substrate 50, and may have a multi-layer structure, wherein at least one silicon oxide (SiO_(x)) layer and at least one silicon nitride (SiN_(x)) layer are alternately stacked on each other. The barrier layer 100 forms a flat surface on the plastic substrate 50 and blocks unwanted substances, such as oxygen and moisture, from penetrating through the plastic substrate 50. The barrier layer 100 may be formed using a plasma enhanced chemical vapor deposition (PECVD) method using plasma. However, forming the barrier layer 100 is not limited thereto, and any deposition method may be used, such as an atmospheric pressure CVD (APCVD) method or a low pressure CVD (LPCVD) method. According to an embodiment of the present invention, the barrier layer 100 is formed at high temperature so that the barrier layer 100 is thin, has a uniform stress, and has a high film density. Specifically, in embodiments, since the plastic substrate 50 having a high Tg is used, the barrier layer 100 may be formed at high temperature.

In embodiments, the barrier layer 100 is formed at a temperature from about 350° C. to about 400° C. Accordingly, the barrier layer 100 may be formed to have a uniform film stress, a thin thickness, and a high film density to effectively block moisture and oxygen. Characteristics of the barrier layer 100 will now be described in detail.

Referring to FIG. 1, the barrier layer 100 according to the current embodiment of the present invention includes a first silicon oxide layer 101 formed on the plastic substrate 50, a first silicon nitride layer 201 formed on the first silicon oxide layer 101, and a second silicon oxide layer 102 formed on the first silicon nitride layer 201. Here, the first and second silicon oxide layers 101 and 102 may each have a film stress from about −100 MPa to about −300 MPa, and the first silicon nitride layer 201 may have a film stress from about −50 MPa to about 200 MPa. The film stress denotes a size of strength of a thin film layer per unit area, and may be compressive film stress or tensile film stress. Here, the compressive film stress is indicated with a negative integer, and the tensile film stress is indicated with a positive integer. Also, the compressive film stress may be power pushing a thin film to bend the thin film downward. On the other hand, the tensile film stress may be power pulling a thin film to bend the thin film upward.

In embodiments, each of the first and second silicon oxide layers 101 and 102 may have compressive film stress, and the first silicon nitride layer 201 may have tensile film stress. Accordingly, with the structure, in which the first silicon oxide layer 101, the first silicon nitride layer 201, and the second silicon oxide layer 102 are alternatively stacked and have different types of film stresses, the barrier layer 100 becomes strong against external shock or bending. Also, the substrate 1000 does not affect a thin film transistor and an electronic device disposed on the barrier layer 100 in terms of stress.

The barrier layer 100 has a film stress from about −200 MPa to about 200 MPa. When the film stress of the barrier layer 100 is below about −200 MPa or above about 200 MPa, the substrate 1000 including the barrier layer 100 may bend upward or downward. In this case, the substrate 1000 may be stuck in an equipment during transference or operation. Also, when the film stress of the barrier layer 100 is below about −200 MPa or above about 200 MPa, dislocation may be generated at an interface between a top surface of the barrier layer 100 and another thin film disposed on the top surface of the barrier layer 100 due to an excessive stress. Such dislocation deteriorates characteristics of the thin film transistor and the electronic device disposed on the barrier layer 100. Besides, film quality of the other film disposed on the barrier layer 100 may deteriorate, thereby deteriorating electric characteristics of the electronic device or causing a defect in the electronic device. Alternatively, the barrier layer 100 may have a film stress of about 0 MPa, because the film stress of the barrier layer 100 may be counterbalanced as the first and second silicon oxide layers 101 and 102, and the first silicon nitride layer 201 have different film stresses. Accordingly, even when the barrier layer 100 has the film stress of 0 MPa, each of the first and second silicon oxide layers 101 and 102 and the first silicon nitride layer 201 still has film stress.

Also, The thickness of the first silicon nitride layer 201 may be from about 200 Å to about 1000 Å. Here, the thickness of the first silicon nitride layer 201 is about 200 Å or above since 200 Å is a minimum thickness for forming a thin film. The thickness of the first silicon nitride layer 201 is limited to about 1000 Å or below due to the following reason. When the first silicon nitride layer 201 is formed at high temperature, hydrogen atoms are separated and escape from the first silicon nitride layer 201 as coherence between silicon atoms and the hydrogen atoms decreases, and thus a hydrogen atom content in the first silicon nitride layer 201 decreases. Accordingly, film stress of the first silicon nitride layer 201 changes from compressive film stress to tensile film stress. At this time, when the thickness of the first silicon nitride layer 201 exceeds 1000 Å, the first silicon nitride layer 201 may break or be detached.

In embodiments, each of the first and second silicon oxide layers 101 and 102 may have a thickness from about 1000 Å to about 3000 Å. When the thickness of each of the first and second silicon oxide layers 101 and 102 is below about 1000 Å, the first and second silicon oxide layers 101 and 102 are difficult to be formed, and when the thickness of each of the first and second silicon oxide layers 101 and 102 is above about 3000 Å, a time taken to form the first and second silicon oxide layers 101 and 102 remarkably increases.

In embodiments, moisture and oxygen penetration may be controlled by the hydrogen atom content in the first silicon nitride layer 201 included in the barrier layer 100.

In embodiments, the first silicon nitride layer 201 is formed at a temperature from about 350° C. to about 400° C. using the PECVD technique as follows. The plastic substrate 50 on which a layer is deposited is put into a chamber, and a process temperature is set to be from about 350° C. to about 400° C. under a plasma atmosphere. The first silicon nitride layer 201 is formed with silane (SiH₄) and ammonia (NH₃). The silane is decomposed into silicon (Si) atoms and hydrogen (H) atoms, and the ammonia is decomposed into nitrogen (N) atoms and hydrogen atoms by plasma. These decomposed silicon, hydrogen, and nitrogen atoms fall onto the plastic substrate 50, and react to form silicon nitride at surface temperature of the plastic substrate 50.

Here, the nitrogen atoms and the hydrogen atoms combine with the silicon atoms. Since coherence between the silicon atoms and the hydrogen atoms is weaker than coherence between the silicon atoms and the nitrogen atoms, even when the silicon atoms and the nitrogen atoms maintain the coherence, the silicon atoms and the hydrogen atoms are separated from each other at high temperature. As a result, the hydrogen atoms separated from the silicon atoms form hydrogen molecules (H₂) and disappear. Accordingly, when the first silicon nitride layer 201 is formed at high temperature, the hydrogen atom content in the first silicon nitride layer 201 is low. Also, as the hydrogen atom content in the first silicon nitride layer 201 decreases, i.e., as the coherence between the nitrogen atoms and silicon atoms increases, the film stress of the first silicon nitride layer 201 becomes more tensile. Also, as the hydrogen atom content in the first silicon nitride layer 201 decreases, film density of the first silicon nitride layer 201 increases.

In embodiments, the hydrogen atom content in the first silicon nitride layer 201 may be from about 13% to about 17%, because the hydrogen atom content in the first silicon nitride layer 201 depends on the temperature of forming silicon nitride. Experimentally, when a silicon nitride layer is deposited at a temperature from about 350° C. to about 400° C., hydrogen atom content in the silicon nitride layer is from about 13% to about 17%. Also, if the hydrogen atom content in the first silicon nitride layer 201 is below about 13%, film density of the first silicon nitride layer 201 may increase, but tensile film stress of the first silicon nitride layer 201 increases above a threshold value and thus a stress balance of the barrier layer 100 may break. On the other hand, if the hydrogen atom content in the first silicon nitride layer 201 is above about 17%, the film density of the first silicon nitride layer 201 may remarkably decrease, and thus unwanted substances, such as oxygen and moisture, may penetrate into the thin film transistor and the electronic device.

In embodiments, he film density of the first silicon nitride layer 201 may be from about 2.5 g/cm³ to about 2.7 g/cm³, The film density of the first silicon nitride layer 201 depends on the hydrogen atom content in the first silicon nitride layer 201. When the hydrogen atom content in the first silicon nitride layer 201 is from about 13% to about 17%, the film density of the first silicon nitride layer 201 may be from about 2.5 g/cm³ to about 2.7 g/cm³. If the film density of the first silicon nitride layer 201 is below about 2.5 g/cm³, the function of the first silicon nitride layer 201 for blocking impure elements, such as oxygen and moisture, from penetrating into the thin film transistor and the electronic device may remarkably deteriorate. On the other hand, the film density of the first silicon nitride layer 201 is difficult to exceed about 2.7 g/cm³ if the hydrogen atom content is from about 13% to about 17%.

FIG. 2 is a cross-sectional view of a substrate 1000 a for a flexible display, according to another embodiment of the present invention. Referring to FIG. 2, the substrate 1000 a is similar to the substrate 1000 as at least one silicon oxide layer and at least one silicon nitride layer are alternately stacked on the plastic substrate 50. However, barrier layer 100 a of the substrate 1000 includes the first silicon oxide layer 101, the first silicon nitride layer 201 disposed on the first silicon oxide layer 101, the second silicon oxide layer 102 disposed on the first silicon nitride layer 201, a second silicon nitride layer 202 disposed on the second silicon oxide layer 102, and a third silicon oxide layer 103 disposed on the second silicon nitride layer 202. Here, discussions of the barrier layer 100 of FIG. 1 are all applicable to the barrier layer 100 a. Specifically, the characteristics of the barrier layer 100 of FIG. 1 are all applicable to the characteristics of the barrier layer 100 a, including thicknesses, types of film stresses, contents of hydrogen atoms, film densities. Also, the method of making the oxide layers 101, 102 and nitride layer 202 of the embodiment of FIG. 1 and conditions of forming these layers are also applicable to the embodiment of FIG. 2. Thus, the discussions are not repeated.

FIG. 3 is a cross-sectional view of a substrate 1000 b for a flexible display, according to another embodiment of the present invention. Referring to FIG. 3, the substrate 1000 b is similar to the substrates 1000 and 1000 a as at least one silicon oxide layer and at least one silicon nitride layer are alternately stacked on the plastic substrate 50. However, barrier layer 100 b of the substrate 1000 b includes the first silicon oxide layer 101, the first silicon nitride layer 201 disposed on the first silicon oxide layer 101, the second silicon oxide layer 102 disposed on the first silicon nitride layer 201, the second silicon nitride layer 202 disposed on the second silicon oxide layer 102, the third silicon oxide layer 103 disposed on the second silicon nitride layer 202, a third silicon nitride layer 203 disposed on the third silicon oxide layer 103, and a fourth silicon oxide layer 104 disposed on the third silicon nitride layer 203. Here, discussions of the barrier layer 100 of FIG. 1 are all applicable to the barrier layer 100 b. Specifically, the characteristics of the barrier layer 100 of FIG. 1 are all applicable to the characteristics of the barrier layer 100 b, including thicknesses, types of film stresses, contents of hydrogen atoms, film densities. Also, the method of making the oxide layers 101, 102 and nitride layer 202 of the embodiment of FIG. 1 and conditions of forming these layers are also applicable to the embodiment of FIG. 3. Thus, the discussions are not repeated.

FIGS. 4 through 6 are diagrams for describing a method of manufacturing a display device by using the substrate 1000 of FIG. 1, according to an embodiment of the present invention. Specifically, FIGS. 4 and 5 are diagrams for describing a method of manufacturing the substrate 1000. For the convenience of description, only the method used for the substrate 1000 is described. However, the same method will also be applied to the substrates 1000 a and 1000 b.

Referring to FIG. 4, first, the plastic substrate 50 is prepared. The Tg of the plastic substrate 50 may be from about 350° C. to about 500° C. so that the plastic substrate 50 stand high temperature treatments.

Referring to FIG. 5, the barrier layer 100 is formed on the plastic substrate 50. Here, the barrier layer 100 is formed at a temperature from about 350° C. to about 400° C. according to a PECVD method. In detail, the barrier layer 100 includes the first silicon oxide layer 101 formed on the plastic substrate 50, the first silicon nitride layer 201 formed on the first silicon oxide layer 101, and the second silicon oxide layer 102 formed on the first silicon nitride layer 201. Here, the thickness of each of the first and second silicon oxide layers 101 and 102 is from about 1000 Å to about 3000 Å, and the thickness of the first silicon nitride layer 201 is from about 200 Å to about 1000 Å. Each of the first and second silicon oxide layers 101 and 102 has compressive film stress, and the first silicon nitride layer 201 has tensile film stress. Also, the film stress of the barrier layer 100 is from about −200 MPa to about 200 MPa. Here, if the film stress of the barrier layer 100 is outside the above range, the substrate 1000 could bend, or dislocation could occur in the interface between the barrier layer 100 and a device that is formed on the barrier layer 100 due to the film stress.

In embodiments, the first silicon nitride layer 201 included in the barrier layer 100 may be formed at a temperature from about 350° C. to about 400° C. according to a PECVD method, by using silane and ammonia. In embodiments, the first silicon nitride layer 201 formed as described above has a hydrogen atom content from about 13% to about 17%, and a film density from about 2.5 g/cm³ to about 2.7 g/cm³, In embodiments, when the hydrogen atom content in the first silicon nitride layer 201 is from about 13% to about 17%, the film density of the first silicon nitride layer 201 may be from about 2.5 g/cm³ to about 2.7 g/cm³ and the first silicon nitride layer 201 may block moisture and oxygen suitably to manufacture the display device.

Referring to FIG. 6, in embodiments, a semiconductor active layer 10, including a source region 10 s, a drain region 10 d, and a channel region 10 c, is patterned and formed on the barrier layer 100, and a first insulation layer 11 is formed on the semiconductor active layer 10. A gate electrode 20 g corresponding to the semiconductor active layer 10 is formed on the first insulation layer 11, and a second insulation layer 12 is formed on the gate electrode 20 g. A contact hole (not shown) is formed in the first and second insulation layers 11 and 12, and a source electrode 20 s and a drain electrode 20 d are formed on the second insulation layer 12 and are electrically connected to the semiconductor active layer 10 through the contact hole, thereby completing the manufacture of a thin film transistor. Also, although not illustrated in FIG. 6, a flexible display may be manufactured by further forming a capacitor and an electronic device such as an organic light emitting device (OLED).

When the barrier layer is not formed at high temperature, the silicon oxide layer and silicon nitride layer may need to be thick so as to prevent moisture and oxygen from penetrating. Alternatively, when the barrier layer is formed at a low temperature, particles of the barrier layer are loose, and thus film stress of the barrier layer is high and a hydrogen atom content is high. Accordingly, film density of the barrier layer is low. As a result, when the barrier layer is formed at low temperature, the barrier layer may have a high film stress, and thus a thin film transistor and an electronic device are adversely affected, moisture and oxygen blocking characteristics are low. However, according to embodiments of the present invention, these can be resolved by forming the barrier layer at high temperature and with the use of a plastic substrate having a high Tg.

FIG. 6 illustrates a top gate thin film transistor that can be formed over a barrier layer according to embodiments of the invention. However, alterntatively a bottom gate thin film transistor can be formed similarly. Also, only one thin film transistor is shown in FIG. 6, but this is only for convenience of description, and a plurality of thin film transistors, a plurality of capacitors, or a plurality of OLEDs may be included.

In addition, in FIG. 6, the substrate 1000 is used as a lower substrate formed below the thin film transistor and the electronic device, but the substrate 1000 may also be disposed in an encapsulating member. In other words, the encapsulating member including the substrate 1000 is separately formed, and the encapsulating member is combined to an OLED, thereby easily encapsulating the OLED.

Also, the substrate 1000 may be used for any one of various flat display devices, such as organic light emitting display devices and liquid crystal display devices.

According to a substrate for a flexible display and a method of manufacturing the substrate according to one or more embodiments of the present invention, a barrier layer is formed on a plastic substrate at high temperature, and thus the substrate having a thin thickness and film stress range that does not adversely affect a thin film transistor and an electronic device may be provided.

Also, the barrier layer includes a silicon nitride layer that has a low hydrogen atom content in the silicon nitride layer. Thus, the silicon nitride layer has a high film density, thereby highly efficiently blocking moisture and oxygen penetration.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims. 

1. A flexible substrate, comprising: a plastic substrate having a glass transition temperature from about 350° C. to about 500° C.; and a barrier layer disposed on the plastic substrate, having a multi-layer structure, which comprises at least one silicon oxide layer and at least one silicon nitride layer that are alternately stacked on each other, the barrier layer having a film stress from about −200 MPa to about 200 MPa.
 2. The substrate of claim 1, wherein the barrier layer comprises: a first silicon oxide layer; a silicon nitride layer stacked on the first silicon oxide layer; and a second silicon oxide layer stacked on the silicon nitride layer.
 3. The substrate of claim 1, wherein the barrier layer comprises: a first silicon oxide layer; a first silicon nitride layer stacked on the first silicon oxide layer; a second silicon oxide layer stacked on the first silicon nitride layer; a second silicon nitride layer stacked on the second silicon oxide layer; and a third silicon oxide layer stacked on the second silicon nitride layer.
 4. The substrate of claim 1, wherein the barrier layer comprises: a first silicon oxide layer; a first silicon nitride layer stacked on the first silicon oxide layer; a second silicon oxide layer stacked on the first silicon nitride layer; a second silicon nitride layer stacked on the second silicon oxide layer; a third silicon oxide layer stacked on the second silicon nitride layer; a third silicon nitride layer stacked on the third silicon oxide layer; and a fourth silicon oxide layer stacked on the third silicon nitride layer.
 5. The substrate of claim 1, wherein the at least one silicon oxide layer has compressive film stress, and wherein the at least one silicon nitride layer has tensile film stress.
 6. The substrate of claim 1, wherein a film density of the at least one silicon nitride layer is from about 2.5 g/cm³ to about 2.7 g/cm³.
 7. The substrate of claim 1, wherein a hydrogen atom content in the at least one silicon nitride layer is from about 13% to about 17%.
 8. The substrate of claim 1, wherein a thickness of each of the at least one silicon nitride layer is from about 200 Å to about 1000 Å.
 9. The substrate of claim 1, wherein a thickness of each of the at least one silicon oxide layer is from about 1000 Å to about 3000 Å.
 10. The substrate of claim 1, wherein the plastic substrate comprises polyimide.
 11. A method of manufacturing a flexible substrate, the method comprising: providing a plastic substrate having a glass transition temperature from about 350° C. to about 500° C.; and forming a barrier layer having a film stress from about −200 MPa to about 200 MPa by alternately stacking at least one silicon oxide layer and at least one silicon nitride layer on the plastic substrate.
 12. The method of claim 11, wherein the forming of the barrier layer comprises forming the barrier layer using a high temperature deposition technique at a temperature from about 350° C. to about 400° C.
 13. The method of claim 11, wherein the barrier layer comprises: a first silicon oxide layer; a silicon nitride layer stacked on the first silicon oxide layer; and a second silicon oxide layer stacked on the silicon nitride layer.
 14. The method of claim 11, wherein the barrier layer comprises: a first silicon oxide layer; a first silicon nitride layer stacked on the first silicon oxide layer; a second silicon oxide layer stacked on the first silicon nitride layer; a second silicon nitride layer stacked on the second silicon oxide layer; and a third silicon oxide layer stacked on the second silicon nitride layer.
 15. The method of claim 11, wherein the barrier layer comprises: a first silicon oxide layer; a first silicon nitride layer stacked on the first silicon oxide layer; a second silicon oxide layer stacked on the first silicon nitride layer; a second silicon nitride layer stacked on the second silicon oxide layer; a third silicon oxide layer stacked on the second silicon nitride layer; a third silicon nitride layer stacked on the third silicon oxide layer; and a fourth silicon oxide layer stacked on the third silicon nitride layer.
 16. The method of claim 11, wherein the at least one silicon oxide layer has compressive film stress, and wherein the at least one silicon nitride layer has tensile film stress.
 17. The method of claim 11, wherein a film density of the at least one silicon nitride layer is from about 2.5 g/cm³ to about 2.7 g/cm³.
 18. The method of claim 11, wherein a hydrogen atom content in the at least one silicon nitride layer is from about 13% to about 17%. 